1. Field of the Invention
The present invention relates to a frequency multiplier, a dielectric transmission line device, and a radio device, for use in a high frequency range such as a millimeter wave or sub-millimeter wave range.
2. Description of the Related Art
A signal source having a sufficiently high capability of directly generating a signal in the millimeter wave or sub-millimeter wave range is not known in the art. Therefore, in the millimeter wave or sub-millimeter wave range, frequency multipliers are widely used to generate a signal at a desired frequency by multiplying the frequency of an input signal by an integral factor. Frequency multipliers are generally realized using non-linearity in the current vs. voltage characteristic of a device such as a Schottky barrier diode, step recovery diode, bipolar transistor, FET, etc.
FIG. 6 illustrates a conventional frequency multiplier. As shown in FIG. 6, the frequency multiplier includes an FET for generating a multiplied frequency, an input matching circuit disposed between an input terminal and the FET, and an output matching circuit disposed between the FET and an output terminal. The frequency multiplier is designed taking into account both the fundamental-frequency signal input via the input terminal and the multiplied-frequency signal output via the output terminal. For example, the output matching circuit is designed such that the signal at the fundamental frequency is absolutely reflected but, at a desired harmonic frequency, a signal having a maximum power is transferred to the output terminal. In FIG. 6, a fundamental frequency reflecting stub reflects the fundamental frequency and a multiplied frequency matching stub provides matching with the FET so that the multiplied frequency is output in a most efficient manner.
In the conventional frequency multiplier, as shown in FIG. 6, input and output matching circuits with a large size and a complicated structure are required to provide matching for both the fundamental frequency and the multiplied frequency. In circuits used in the millimeter or sub-millimeter wave ranges, a dielectric transmission line such as an NRD (Non-Radiative Dielectric) waveguide is known to be advantageous in that a low transmission loss can be achieved. However, in practice, no frequency multiplier is known which provides an output signal directly through a NRD waveguide.
In order to output a signal via an NRD waveguide, it is required to provide a transmission line transformer between a conventional type frequency multiplier with a microstrip line and the NRD waveguide as shown in FIG. 7. However, when the output matching circuit is constructed in the form of a planar circuit as shown in FIG. 6, a transmission line transformer circuit for providing a connection between the planar circuit and the NRD waveguide is needed to be connected to the output terminal of the frequency multiplier. This causes the frequency multiplier to become greater in total size and more complex in structure.
In view of the above, it is an object of the present invention to provide a frequency multiplier with an output matching circuit having a simplified structure in which an output signal is obtained directly through a dielectric transmission line.
It is another object of the present invention to provide a dielectric transmission line device in which a small-sized frequency multiplier is employed so as to achieve a reduction in the total size.
It is still another object of the present invention to provide a radio device using a dielectric transmission line of the above-described type as a transmission line for transmitting a transmission signal.